The Potyviridae family is characterized by a positive sense single stranded RNA genome and a flexuous elongated particle measuring 650 to 900 nm in length. Potyviruses are found worldwide and can cause substantial disruption to host plant growth and development either from single infection or synergistically during coinfection with other viruses (Hull R, Mathews' Plant Virology, Academic Press (2001); Shukla et al., The Potyviridae. CAB International, Wallingford (1994). To address the challenges that potyviruses have posed to pepper and tomato production, plant breeders have utilized a number of recessively inherited resistance sources.
In pepper, resistance allele pvr1 was discovered in two accessions of Capsicum chinense and is effective against particular strains of Potato virus Y (PVY), Tobacco etch virus (TEV), and Pepper mottle virus (PepMoV). Allele pvr11 was discovered in two cultivated varieties of Capsicum annuum and is known to confer resistance against only a few strains of PVY. Resistance allele pvr12 was discovered in two accessions of Capsicum annuum. It provides resistance against a broad range of PVY and TEV strains. Natural virus resistance within Capsicum has proven somewhat difficult to breed with due to its recessive inheritance but continues to be highly durable and effective even after decades of commercial use. In tomato, the virus resistance allele pot-1 was identified in Solanum habrochaites (formerly Lycopersicon hirsutum) (Parrella et al., “Recessive Resistance Genes Against Potyviruses are Localized in Colinear Genomic Regions of the Tomato (Lycopersicon spp.) and Pepper (Capsicum spp.) Genomes,” Theor Appl Genet. 105:855-861 (2002)). This recessive resistance gene has been shown to provide resistance against both Tobacco etch virus (TEV) and Potato virus Y (PVY).
The pvr1 and pot-1 loci of pepper and tomato, respectively, have been shown to encode orthologous copies of the eukaryotic translation initiation factor 4E (eIF4E), a protein involved in binding to the 5′ cap of messenger RNA and aiding in recruitment to the host ribosomal complex (Gingras et al., “eIF4 Initiation Factors: Effectors of mRNA Recruitment to Ribosomes and Regulators of Translation,” Annu Rev Biochem 68:913-63 (1999); Kang et al., “The pvr1 Locus in Capsicum Encodes a Translation Initiation Factor eIF4E that Interacts with Tobacco Etch Virus VPg,” Plant J 42:392-405 (2005); Ruffel et al., “A Natural Recessive Resistance Gene Against Potato Virus Y in Pepper Corresponds to the Eukaryotic Initiation Factor 4E (eIF4E),” Plant J 32:1067-75 (2002); Ruffel et al., “The Recessive Potyvirus Resistance Gene Pot-1 is the Tomato Orthologue of the Pepper pvr2-eIF4E Gene,” Mol Genet Genomics 274:346-53 (2005)). During viral infection, eIF4E has been shown to bind to the viral genome-linked protein (VPg) (Leonard et al., “Complex Formation Between Potyvirus VPg and Translation Eukaryotic Initiation Factor 4E Correlates with Virus Infectivity,” J Virol 74:7730-7 (2000); Schaad et al., “Strain-Specific Interaction of the Tobacco Etch Virus NIa Protein with the Translation Initiation Factor eIF4E in the Yeast Two-hybrid System,” Virology 273:300-6 (2000)). eIF4E binding with VPg is thought to facilitate translation of the virus genome, replication of the virus genome, and/or cell-to-cell movement of the virus (Gao et al., “The Potyvirus Recessive Resistance Gene, sbm1, Identifies a Novel Role for Translation Initiation Factor eIF4E in Cell-To-Cell Trafficking,” The Plant Journal 40:376-385 (2004); Kang et al., “The pvr1 Locus in Capsicum Encodes a Translation Initiation Factor eIF4E that Interacts with Tobacco Etch Virus VPg,” Plant J 42:392-405 (2005); Robaglia et al., “Translation Initiation Factors: A Weak Link in Plant RNA Virus Infection,” Trends Plant Sci 11:40-5 (2006)). Resistant alleles of eIF4E differ from wildtype sequences by only a few amino acid changes. Resistant versions of eIF4E disrupt the interaction with VPg, which often leads to strain-specific virus resistance.
In addition to pepper and tomato, recessive resistance alleles at the eIF4E locus have been identified in lettuce (Nicaise et al., “The Eukaryotic Translation Initiation Factor 4E Controls Lettuce Susceptibility to the Potyvirus Lettuce Mosaic Virus,” Plant Physiol 132:1272-82 (2003)), barley (Stein et al., “The Eukaryotic Translation Initiation Factor 4E Confers Multiallelic Recessive Bymovirus Resistance in Hordeum Vulgare (L.),” Plant J 42:912-22 (2005)), pea (Gao et al., “The Potyvirus Recessive Resistance Gene, sbm1, Identifies a Novel Role for Translation Initiation Factor eIF4E in Cell-To-Cell Trafficking,” The Plant Journal 40:376-385 (2004)), and melon (Nieto et al., “An eIF4E Allele Confers Resistance to an Uncapped and Non-Polyadenylated RNA Virus in Melon,” Plant J 48:452-62 (2006)). However, despite the fact that potyviruses result in significant yield losses in cultivated potato, only dominant potyvirus resistance has been identified in potato to date (Solomon-Blackburn et al., “A Review of Host Major-Gene Resistance to Potato Viruses X, Y, A and V in Potato: Genes, Genetics and Mapped Locations,” Heredity 86:8-16 (2001)).
The present invention is directed to overcoming these and other deficiencies in the art.